If you are having trouble sending emails to Comcast users, and your emails are being rejected with the error code BL000000 from the recipient server, it means that your sending IP address is being blacklisted on Comcast’s internal blacklist system. This means that none of your emails will go through to the Comcast users until you fix the issues that got you blacklisted and until you request delisting from their blacklist.

The exact error that you would be seeing in your logs is:

BL000000 Email from your mail server has been sent in patterns that are characteristic of spam.

If the error code is anything other than BL000000, then further instructions should be provided in the error message, along with a link explaining that certain error code.

Before starting the delisting procedure:

  1. First and foremost you should do a Blacklist Check for your IP address and make sure it isn’t blacklisted on any other public RBLs. This is very important to know, because if your IP is blacklisted in other blacklists, you will need to delist it from there first (by following the delisting procedures for each individual blacklist, and then waiting for them to delist your IP address), and only then proceed with the Comcast blacklist removal process. If your IP address isn’t blacklisted anywhere else, you can proceed to step 2 of this guide.
  2. This next step is just as important as the first one. You will need to make sure that you’ve cleaned/fixed the issue that got you blacklisted in the first place. For instance: if your server was infected by malware and was sending out spam emails, be sure to have it cleaned before proceeding with the delisting procedures. Another example would be: if your domain or email server wasn’t respecting RFC standards or was missing basic standards such as rDNS, etc., make sure you fix that as well.
  3. Make sure your email server isn’t going over the Comcast sending limits, which are:
    – max 25 simultaneous connections from each individual sending IP address
    – max 100 recipients for each individual email message
    – your IP address reputation may impact these limits
  4. Read and comply with everything listed on their guide: What Do I Need to Know to Avoid Blocks When Sending to Comcast?

Delisting your IP address:

  1. You will need to be the email administrator and be able to provide technical information in the delisting form.
  2. Proceed by filling in the delisting request form on their website:
    (make sure all the info is accurate and to the point)
    Request form limits apply:
    – you cannot request delisting of the same IP address more than 5 times per day
    – you can request a maximum of 20 different IP addresses to be delisted per day
  3. In most cases, if your delisting request is properly filled in, the block will be lifted within 30 minutes of your delisting request submission. However, in some cases the block cannot be lifted unless you contact the Comcast Customer Security Assurance at the following phone number: 888-565-4329

Final Notes:

  • If you do not delist your IP address from all other public RBLs before requesting delisting from Comcast, it’s most likely that they will not lift your block; or if they do lift it, it’s most likely that your IP address will just end up being blocked again in no time.
  • The same as above applies to the situations where you do not fix the issue(s) that got you blacklisted in the first place. This is very important if you wish for your IP address to remain clean after being delisted from any blacklist, not just from the Comcast blacklist.
  • If the Comcast email servers give out any errors other than BL000000, you should check out their error explanation page to understand what those errors mean: https://www.xfinity.com/support/articles/email-errors
  • It’s always a good idea to constantly blacklist monitor all of your IP addresses to know as soon as they get listed on any public RBL. You can use our platform to do just that. We do not monitor the Comcast blacklist (since it is private, and only Comcast has access to it), but it is still a very good indicator to know if/when any public RBL will blacklist your IP addresses. If your IPs start getting blacklisted on public RBLs, then it’s most likely they are blacklisted on private RBLs (such as the Comcast blacklist) as well.